Method for producing light gypsum board

ABSTRACT

Provided is a method of manufacturing a weight-saved foamed gypsum board having a gypsum core with high strength and excellent adhesion properties of the gypsum core with base papers for gypsum board, which method is capable of adjusting the sizes of pores in a gypsum core of a weight-saved gypsum board product into a desired range in a short time and at a low cost, even if the kinds and the compounding ratios of gypsum raw materials vary. The method of manufacturing a weight-saved gypsum board in which pores with a predetermined size are distributed in a gypsum core, includes the steps of blowing air into a foaming agent to produce foams, mixing the foams into a kneaded material that contains calcined gypsum and water to obtain foamed gypsum slurry, pouring the foamed gypsum slurry into a space between upper and lower base papers for gypsum board, shaping the base papers and the foamed gypsum slurry into a board shape, roughly cutting off and subsequently drying the board-shaped one, and cutting off the dried and shaped one into a product dimension, wherein the method further comprises the step of preliminarily adding a pore size adjusting agent for adjusting sizes of foams distributed in the foamed gypsum slurry to one of a stock solution of the foaming agent and a mixture of a stock solution of the foaming agent and water to obtain the foaming agent for producing foams with desired sizes.

TECHNICAL FIELD

The present invention relates to a method of manufacturing aweight-saved foamed gypsum board (hereinafter called “a weight-savedgypsum board”) having a gypsum core with high strength and excellentadhesion properties of the gypsum core with base papers for gypsumboard. More particularly, the present invention relates to a method ofmanufacturing a weight-saved gypsum board, capable of adjusting thesizes of pores in a gypsum core of a weight-saved gypsum board productinto a desired range in a short time and at a low cost, even if thekinds and the compounding ratios of gypsum raw materials vary.

BACKGROUND ART

A gypsum board is a representative gypsum-based building material.Commonly, gypsum board is manufactured according to the following steps.First, foams are preliminarily produced by blowing air into a foamingagent for weight-saving the gypsum board. Then, foams produced from thefoaming agent are mixed into a kneaded material that contains a calcinedgypsum, an adhesive, various additives and water using a mixer so as toprepare a foamed gypsum slurry to be used as a gypsum core. Then, theprepared foamed gypsum slurry is poured into a space between upper andlower base papers for gypsum board and covered with the base papers forgypsum board. Then, the gypsum slurry covered with the base papers forgypsum board passes through a shaping machine for determining thethickness and width of a gypsum board so as to be shaped into apredetermined board shape. Subsequently, the strip-type original gypsumboard that is shaped into a board shape is roughly cut off and passesthrough a force-drying machine. Finally, the original board after thedrying is cut off to a predetermined dimension for a gypsum boardproduct. That is, the gypsum board is a board-shaped structure, in whicha gypsum core obtained by the above-mentioned pouring and shaping methodis covered with base papers for gypsum board, and has excellent fireresistance, sound insulation, workability and economical efficiency.

In recent years, gypsum board has been used as an interior material inhigh-rise or super high-rise buildings that are spreading rapidly, aswell as in general buildings and low-rise or middle-rise buildings.Gypsum board is known to have excellent properties in regard toadaptability to a building process, weight saving for a building, andflexibility against building oscillation. The weight saving for a gypsumboard primarily depends on the ratio of gypsum being a gypsum corematerial and pores formed by foam, and the less the amount of the gypsumis, that is, the more the amount of the pores formed by the foams, theweight saving is further advanced. However, a reduction in the amount ofgypsum may cause the strength of the gypsum core to lower and failure ofthe adhesion of the gypsum core with the base paper for gypsum board soas to degrade the commercial value of the gypsum board product. Thus,the amount of gypsum is consequentially decided and the weight savingfor the gypsum board is limited.

Methods for manufacturing a gypsum board have been studied such that thegypsum board is weight-saved while the strength of the gypsum board ismaintained by changing the structure and distribution condition of poresin the gypsum core. As an example of such studies, conventionally, foamsobtained by blowing air into a foaming agent exhibiting excellentstability are mixed into a gypsum slurry so as to produce many smallpores in the gypsum core, thereby achieving the weight saving for thegypsum board. However, recently, a modification technique for a gypsumcore has been proposed which can achieve the weight saving for thegypsum board by containing relatively large independent pores uniformlyin the gypsum core.

Such a modification technique for a gypsum core is disclosed in JapanesePatent No. 3028123, in which foams with a desired density are preparedusing an aqueous solution of a foaming agent stock solution thatcontains a particular alkyl ether sulfate and the foams are mixed withgypsum slurry so as to distribute independent large pores uniformly in agypsum core. Also, a technique whereby foams are produced from a mixtureobtained by mixing a particular alkyl ether sulfate as the first foamingagent for forming stable foams in gypsum slurry and a particular alkylsulfate as the second foaming agent for forming unstable foams in thegypsum slurry with the mixing ratio in a desired range and the mixtureof the foaming agent is stirred and mixed with the gypsum slurry, so asto contain relatively large independent pores in a gypsum core, isdisclosed in U.S. Pat. No. 5,643,510. Additionally, a technique wherebycontaining fine pores in a gypsum foamed core is suppressed as much aspossible and pores formed by relatively large independent foams aredispersed uniformly by containing a foam stabilizer as well as foams ingypsum slurry for forming the gypsum core is disclosed in JapaneseLaid-Open Patent Application No. 10-330174.

In Japan, a gypsum board has conventionally been manufactured using acalcined gypsum obtained by compounding a variety of chemical gypsumssuch as phosphogypsum, flue gas desulfurized gypsum, neutralized gypsum,and waste recycle gypsum (a gypsum that can be recycled and obtained byscrapping waste materials such as gypsum building materials and gypsummodels) and natural gypsum and by calcining a gypsum material thatcontains the gypsum raw material. However, the sizes and thedistribution condition of the pores distributed in a gypsum core aresignificantly influenced by the kinds and compounding ratios of theabove-mentioned gypsum raw materials. In a production plant for gypsumboard, the proper gypsum raw materials to use in the plant cannot befreely selected from the various gypsum raw materials and use has to bemade according to the fields and demand-supply balance of the respectivegypsum raw materials. Consequently, the kinds and compounding ratios ofthe gypsum raw materials for the gypsum core directly influence thequality of the gypsum board product and have been a particularly seriousproblem.

Another problem is that the compounding ratios of the gypsum rawmaterials vary due to various factors so as to effect a bad influence onthe pore sizes in the gypsum core in sequential processes from thereceipt of the above-mentioned various gypsum raw materials to themanufacture of the gypsum board in the production plant for gypsumboard.

In the process of preparing foamed gypsum slurry and the process ofshaping a gypsum core, it is difficult to detect the influence of thevariations in the kinds and compounding ratios of used gypsum rawmaterials timely. It is also difficult to form independent pores with adesired size steadily and stably in the gypsum core of the gypsum boardproduct, due to the variations in the kinds and compounding ratios ofthe gypsum raw materials. Sometimes, innumerable communicated fine poresmay be formed in a cross section of the gypsum core, so that thestrength of the gypsum core is lowered. An extremely large independentpore may be formed in a cross section of the gypsum core so that thevisual appearance of the gypsum board is problematic, and partialpeeling of a base paper for gypsum board from the gypsum core, called acluster or blister, may occur.

For the gypsum core modification techniques disclosed in U.S. Pat. No.5,643,510 and Japanese Patent No. 3028123, the bad influences of thevariety of the gypsum raw materials on the formation of the pores arenot discussed and the formation of the gypsum core from a single gypsumraw material is presumed. Accordingly, it is known that if thesetechniques are applied to a method for manufacturing a gypsum board inwhich the compounding of a variety of gypsum raw materials is changed,the formation of the pores in the gypsum core is significantlyinfluenced and the sizes and the distribution condition of the pores arewidely changed. Also, in particular, in regard to the techniquedisclosed in U.S. Pat. No. 5,643,510, even if a single gypsum rawmaterial is employed, the average number of moles of ethylene oxideadded to an alkyl ether sulfate is only adjusted and it is clear thatthe range of the controllable sizes of the pores is narrow.

In the gypsum core modification technique disclosed in JapaneseLaid-Open Patent Application No. 10-330174, enough uniformly distributedand relatively large pores can be formed in the gypsum core against thevariation of the kinds and compounding ratios of the gypsum rawmaterials but an addition of a relatively large amount of foamstabilizer is needed, so that the production cost for the gypsum boardis increased.

DISCLOSURE OF THE INVENTION

One of the objects of the present invention is to provide a method ofmanufacturing a weight-saved gypsum board including a gypsum core havinghigh strength and excellent adhesion properties with base papers forgypsum board.

Another object of the present invention is to provide a method ofmanufacturing a weight-saved gypsum board capable of adjusting the sizesof pores in a gypsum core of a weight-saved gypsum board product into adesired range in a short time and at a low cost, even if the kinds andcompounding ratios of gypsum raw materials vary.

The objects of the present invention described above are achieved by amethod of manufacturing a weight-saved gypsum board in which pores witha predetermined size are distributed in a gypsum core, including thesteps of blowing air into a foaming agent to produce a foam havingbubbles, mixing the foam having bubbles into a kneaded material thatcontains calcined gypsum and water to obtain foamed gypsum slurry,pouring the foamed gypsum slurry into a space between upper and lowerbase papers for gypsum board, shaping the base papers and the foamedgypsum slurry into a board shape, roughly cutting off and subsequentlydrying the board-shaped one, and cutting off the dried and shaped oneinto a product dimension, wherein the method further comprises the stepof preliminarily adding a pore size adjusting agent for adjusting sizesof pores formed by bubbles distributed in the foamed gypsum slurry toone of a stock solution of the foaming agent and a mixture of a stocksolution of the foaming agent and water to obtain the foaming agent forproducing a foam having bubbles with pores with desired sizes.

In the method of manufacturing a weight-saved gypsum board, preferably,the pore size adjusting agent contains at least one substance selectedfrom the group including agents for increasing sizes of pores formed bybubbles in the foamed gypsum slurry and agents for decreasing sizes ofpores formed by bubbles in the foamed gypsum slurry.

In the method of manufacturing a weight-saved gypsum board, preferably,the agent for increasing sizes of pores formed by bubbles in the foamedgypsum slurry contains at least one substance selected from the groupincluding water-soluble acidic substances, strong acids, andwater-soluble strong alkaline substances.

In the method of manufacturing a weight-saved gypsum board, preferably,the agent for increasing sizes of pores formed by bubbles in the foamedgypsum slurry contains at least one substance selected from the groupincluding aluminum sulfate, aluminum potassium sulfate, aluminumammonium sulfate, ferric sulfate, polyferric sulfate, sulfuric acid,sulfamic acid, sodium hydroxide, and potassium hydroxide.

In the method of manufacturing a weight-saved gypsum board, preferably,the agent for decreasing sizes of pores formed by bubbles in the foamedgypsum slurry contains at least one substance selected from the groupincluding sulfosuccinate-type surface active agents, sarcosinate-typesurface active agents, alkylbenzene sulfonate-type surface activeagents, alkane sulfonate-type surface active agents, andalkylbetaine-type surface active agents.

In the method of manufacturing a weight-saved gypsum board, preferably,a content of the pore size adjusting agent in the foaming agent is0.00001 parts by weight through 0.005 parts by weight per 100 parts byweight of the calcined gypsum.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings, in which:

FIG. 1 is a view showing pores in a weight-saved gypsum board accordingto reference 1;

FIG. 2 is a view showing pores in the weight-saved gypsum boardaccording to example 1;

FIG. 3 is a view showing pores in the weight-saved gypsum boardaccording to example 2;

FIG. 4 is a view showing pores in the weight-saved gypsum boardaccording to example 3;

FIG. 5 is a view showing pores in the weight-saved gypsum boardaccording to comparison 1;

FIG. 6 is a view showing pores in the weight-saved gypsum boardaccording to reference 2;

FIG. 7 is a view showing pores in the weight-saved gypsum boardaccording to example 4; and

FIG. 8 is a view showing pores in the weight-saved gypsum boardaccording to comparison 2.

BEST MODE FOR CARRYING OUT THE INVENTION

The preferred embodiments of the present invention are described indetail.

A method of manufacturing a weight-saved gypsum board according to thepresent invention is similar to the conventional method of manufacturinga gypsum board except that a pore size adjusting agent is added to afoaming agent and, more specifically, the method is implementedaccording to the following steps. First, foams are produced by blowing(injecting) air into a foaming agent. Then, the foams produced from thefoaming agent are mixed into a kneaded material that contains a calcinedgypsum obtained by calcining a gypsum material that contains a gypsumraw material and water as principal components, so as to prepare foamedgypsum slurry for a gypsum core. Then, the prepared foamed gypsum slurryis poured and spread on a lower side (front-side) base paper for gypsumboard that is continuously delivered, and an upper side (back-side) basepaper for gypsum board is wrapped over the spread foamed gypsum slurry,so that the foamed gypsum slurry is covered with the base papers forgypsum board. Then, the foamed gypsum slurry covered with the basepapers for gypsum board passes through a shaping machine for determiningthe thickness and width of a gypsum board so as to be shaped into apredetermined board-shape. Subsequently, the strip-type original gypsumboard that is shaped into a board shape is roughly cut off. The roughlycut original gypsum board passes through a force-drying machine so as toobtain a dried gypsum core covered with the base papers for gypsumboard. Finally, the gypsum core covered with the base papers for gypsumboard is cut into a desired dimension so as to obtain a weight-savedgypsum board product.

In a method of manufacturing a weight-saved gypsum board according tothe present invention, the foaming agent is obtained by preliminarilyadding a pore size adjusting agent for adjusting the sizes ofindependent foams distributed in the foamed gypsum slurry (or a gypsumcore) into a foaming agent stock solution or a mixture of a foamingagent stock solution and water. The addition of the pore size adjustingagent into a foaming agent stock solution or a mixture of a foamingagent stock solution and water is performed just before producing thefoams from the foaming agent.

According to a method of manufacturing weight-saved gypsum board of thepresent invention, since foams produced from the foaming agent thatcontains the pore size adjusting agent are mixed into the kneadedmaterial that contains the calcined gypsum and water, even if the kindsand compounding ratios of gypsum raw materials vary, the sizes of thepores in the gypsum core of the weight-saved gypsum board product can beadjusted to a desired range in a short time and at a low cost. That is,a gypsum core having a core structure (pore structure), in whichrelatively large sized and approximately spherical-shaped pores areuniformly dispersed, can be obtained. According to a method ofmanufacturing a weight-saved gypsum board of the present invention, amethod of manufacturing a weight-saved gypsum board having a gypsum corewith high strength and excellent adhesion properties of the gypsum corewith the base papers for gypsum board can be provided.

In a method of manufacturing a weight-saved gypsum board according tothe present invention, a method for producing a foam having bubbles ofthe desired size from a foaming agent may be a prefoaming method suchthat air is blown into a foaming agent and is not particularly limited.For implementing the prefoaming method, a mixing apparatus for mixingthe foam having bubbles into the kneaded material has mainly a foamingagent accepting tank for accepting a foaming agent stock solution, apump for pumping a certain amount of the foaming agent stock solutionfrom the foaming agent accepting tank, a foaming apparatus for blowingpressurized air into the foaming agent stock solution pumped from thefoaming agent accepting tank and stirring the mixture of the foamingagent stock solution and the air so as to produce a foam having bubblesfrom the foaming agent stock solution, and at least one pump fordelivering the foams produced from the foaming agent stock solution intoa kneaded material that contains a calcined gypsum and water.

The mixing apparatus may have a water tank for storing water and a pumpfor pumping a certain amount of water from the water tank. In this case,the certain amount of water is preliminarily mixed into the foamingagent stock solution just before the pressurized air is blown into thefoaming agent so as to produce the foams from the foaming agent.

Furthermore, the mixing apparatus may have a dilution tank for dilutingthe foaming agent with water to a predetermined dilution ratio so as toprepare an aqueous solution of the foaming agent stock solution, and apump for pumping a certain amount of the aqueous solution of the foamingagent stock solution. In this case, pressurized air is not blown intothe foaming agent stock solution but the aqueous solution of the foamingagent stock solution is prepared at once and pressurized air is blowninto the aqueous solution of the foaming agent stock solution so thatfoams are produced from the aqueous solution of the foaming agent stocksolution.

As the foaming apparatus, shearing force produced by high-speed stirringmay be further applied to the foaming agent that is provided on thecondition of a stock solution or an aqueous solution and produces foamsusing pressurized air. Alternatively, the foaming agent may pass throughfine particulate beads so as to produce a foam having bubbles fully. Inorder to obtain a certain amount of foams by improving the quantitativeprecision for the foaming agent, the water, and the air, a publiclyknown flowmeter may be provided in the way of a pipeline for deliveringeach substance so as to control the rate of flow of each substanceautomatically.

The foaming agent used for the method of manufacturing a weight-savedgypsum board according to the present invention is not particularlylimited, and anionic, cationic, non-ionic and amphoteric surface activeagents may be used, which agents are conventionally used in themanufacture of gypsum boards and publicly known as air entraining agentsfor cement. The foaming agent is preferably an anionic surface activeagent and more particularly sulfates of alkyls, alkyl aryls, alkylethers, alkyl aryl ethers, poly(oxyethylene) alkyl ethers(poly(ethyleneoxide) alkyl ethers), and poly(oxyethylene)poly(oxypropylene) alkyl ethers (poly(ethyleneoxide)poly(propyleneoxide) alkyl ethers) etc.

In a method of manufacturing a weight-saved gypsum board according tothe present invention, as described above, a foaming agent stocksolution can be used as it is, and an aqueous solution of a foamingagent stock solution that is prepared by diluting the foaming agentstock solution with water preliminarily or just before the foaming canalso be used. When the foaming agent stock solution is diluted withwater, the dilution ratio for the foaming agent stock solution can beset arbitrarily and preferably is within a range of foaming agent stocksolution:water=1:1 through 1:1000. If the dilution ratio is larger thanthe range, the stability of the foams significantly lowers, so thatdefoaming and foam-breaking occur in time of mixing the foam havingbubbles into the kneaded material. As a result, it is difficult todistribute pores uniformly in an obtained gypsum core. On the otherhand, if the dilution ratio is smaller than the range, the loading ofthe foaming agent stock solution is overabundant, so that pressure fordelivering the foaming agent may not be enough and controlling the rateof flow of the foaming agent may be difficult. Additionally, in time ofmixing the foam having bubbles into the kneaded material, a portion ofdefoamed or broken foams may foam up again. As a result, even if thepore size adjusting agent is added into the foaming agent, the sizes ofthe pores in the gypsum core cannot be adjusted.

Next, a pore size adjusting agent is described which is used in a methodof manufacturing a weight-saved gypsum board according to the presentinvention. Such pore size adjusting agent is roughly classified into anagent for increasing the size of foams in foamed gypsum slurry when thesize of the foams in the foamed gypsum slurry is smaller than a desiredsize range, and an agent for decreasing the size of foams in foamedgypsum slurry when the size of the foams in the foamed gypsum slurry islarger than a desired size range.

Herein, the agent for increasing the size of foams in foamed gypsumslurry contains at least one substance selected from the group includingwater-soluble acidic substances, strong acids, and water-soluble strongalkaline substances. The agent for increasing the size of foams infoamed gypsum slurry preferably contains aluminum sulfate, aluminumpotassium sulfate (potassium alum), aluminum ammonium sulfate (ammoniumalum), ferric sulfate, polyvalent metal sulfates such as polyferricsulfate, strong acids such as sulfuric acid and sulfamic acid, andstrong alkalis such as sodium hydroxide and potassium hydroxide, morepreferably the polyvalent metal sulfates.

The agent for decreasing the size of foams in foamed gypsum slurrycontains at least one surface active agent selected from the groupincluding sulfosuccinate-type surface active agents, sarcosinate-typesurface active agents, alkylbenzene sulfonate-type surface activeagents, alkane sulfonate-type surface active agents, andalkylbetaine-type surface active agents.

The pore size adjusting agents are preferably liquid or water-solublesolid. More preferably, the pore size adjusting agent is preliminarilyobtained by mixing and diluting the agent with water. When theconcentration of the aqueous solution of the pore size adjusting agentis too high, even if a small amount of the aqueous solution is addedinto the foaming agent, the changes of the sizes of pores formed bybubbles obtained in the foaming apparatus are too large. As a result,the size of pores in a finally obtained gypsum core become too large ortoo small. Additionally, it becomes very difficult to control the rateof flow of the aqueous solution of the pore size adjusting agent. On theother hand, when the concentration of the aqueous solution of the poresize adjusting agent is too low, the amount of water added into thefoaming agent preliminarily or just before the foaming can be adjustedto some extent. However, the amount of water that is directly kneadedwith the calcined gypsum is reduced. When the aqueous solution of thepore size adjusting agent is prepared, the concentration of the aqueoussolution of the pore size adjusting agent is 10% by weight through 80%by weight, preferably 20% by weight through 70% by weight.

In a method of manufacturing a weight-saved gypsum board according tothe present invention, just before producing a foam having bubbles ofthe desired pore size from the foaming agent, a pore size adjustingagent is poured into a pipeline for delivering the foaming agent stocksolution or the aqueous solution of the foaming agent stock solution.For the pour of the pore size adjusting agent, provided are a pore sizeadjusting agent accepting tank for accepting a pore size adjustingagent, if necessary, a pore size adjusting agent diluting and dissolvingtank for diluting the pore size adjusting agent with water, and a pumpfor pumping the pore size adjusting agent from the pore size adjustingagent diluting and dissolving tank, etc. Such equipment is used to pourthe aqueous solution of the pore size adjusting agent into the foamingagent or into the aqueous solution of the foaming agent deliveredthrough the pipeline. Furthermore, a tube-type mixing apparatus such asa static mixer may be provided on a pipeline portion between the foamingapparatus and the position at which the pore size adjusting agent ispoured into the foaming agent stock solution or the aqueous solution ofthe foaming agent stock solution. In order to keep the loading of thepore size adjusting agent constant, the rate of flow of the pore sizeadjusting agent may be automatically controlled using a publicly knownflowmeter similar to the flowmeter for the foaming agent.

In a method of manufacturing a weight-saved gypsum board according tothe present invention, just before producing a foam having bubbles withthe desired sizes from the foaming agent, the sizes of pores formed bybubbles in the foamed gypsum slurry can be easily controlled byadjusting the loading(s) of the agent for increasing the foam sizesand/or the agent for decreasing the foam sizes to the foaming agentindependently or in combination. Each of the pore size adjusting agentscan be added into the foaming agent independently, in compliance withdesired conditions for foams in the obtained foamed gypsum slurry,particularly, desired sizes of the foams. Additionally, a multiple ofthe pore size adjusting agents can be used in combination and each ofthe loadings of the pore size adjusting agents can also be adjusted. Theloadings of the pore size adjusting agents are not particularly limited,and can be set generally in the range of 0.00001 parts by weight through0.005 parts by weight, preferably in the range of 0.0005 parts by weightthrough 0.003 parts by weight, per 100 parts by weight of calcinedgypsum, regardless of the case of adding the pore size adjusting agentindependently or the case of using a multiple of the pore size adjustingagents in combination.

As a method of adding the pore size adjusting agents into the foamingagent, if the pore size adjusting agents are liquid, the pore sizeadjusting agents can be used as they are or diluted with water for use.If the pore size adjusting agents are solid in powder-form, it isdesirable to dissolve the pore size adjusting agents in water so as toprepare an aqueous solution of suspension of the pore size adjustingagents at once and to add the aqueous solution or suspension into thefoaming agent. Then, an inlet for the pore size adjusting agents isprovided on a pipeline portion for delivering the foaming agent adjacentto the foaming apparatus and the pore size adjusting agents are pouredinto the foaming agent through the inlet. In the flow of the foamingagent, a tube-type mixing apparatus may be provided at the downstreamside of the inlet. When both of the agent for increasing the foam sizesand the agent for decreasing the foam sizes as the pore size adjustingagents or a multiple of the pore size adjusting agents are poured intothe foaming agent delivered in the pipeline, each agent is poured intothe foaming agent through separate inlets or one common inlet.

Thus, the mixture (as the foaming agent) of the pore size adjustingagents and the foaming agent stock solution or the aqueous solution ofthe foaming agent stock solution is delivered into the foaming apparatusand air is injected into the flow of the foaming agent so as to producea foam having bubbles from the foaming agent.

The foams and a kneaded material that contains calcined gypsum and waterare stirred and mixed via a mixing and stirring machine or at a slurryextracting part of the mixing and stirring machine, so that foamedgypsum slurry in which independent foams with a desired size areuniformly distributed can be obtained.

When a method of manufacturing a weight-saved gypsum board according tothe present invention is implemented, just before shaping the foamedgypsum slurry obtained as described above into a board shape in ashaping machine, it is desirable to sample and harden the foamed gypsumslurry regularly so as to obtain a harden foamed gypsum and to confirmthe conditions of pores, particularly pore sizes, in a fracture plane ofthe hardened foamed gypsum. In order to confirm the condition of thepores in the hardened foamed gypsum, a fracture plane of the hardenedfoamed gypsum may be observed by visual observation or by using amagnifier so as to judge whether or not the pores with the desired sizesare formed. Also, whether or not the pores with the desired sizes areformed may be judged by using a publicly known method in which afracture plane of the hardened foamed gypsum is subjected to skew raysand lights and darks of an image on an arbitrary straight line or apredetermined section within a visual field using an imaging device suchas a CCD camera. If the sizes of pores formed by bubbles in the foamedgypsum slurry are too small or smaller than a desired size range, theloading of the agent for increasing the foam sizes is increased withinthe range for the loading. If the sizes of pores formed by bubbles inthe foamed gypsum slurry are too large or larger than the desired sizerange, the agent for decreasing the foam sizes is similarly increased.Accordingly, the sizes of pores formed by bubbles in the foamed gypsumslurry can be adjusted timely and in a short time.

According to a method of manufacturing a weight-saved gypsum board ofthe present invention, even if some kinds of gypsum raw materials arecompounded or only natural gypsum is used, the structure of pores in agypsum core, that is, the size of pores in a gypsum core can be adjustedtimely and freely by mixing foams produced from a foaming agent thatcontains a pore size adjusting agent into gypsum slurry that containswater and calcined gypsum obtained by calcining a gypsum material thatcontains a gypsum raw material.

When aluminum sulfate is used as the pore size adjusting agent by addingand mixing it into a foaming agent just before producing a foam havingbubbles with that desired sizes from the foaming agent, the loading ofit can be significantly reduced compared to the loading of it as a foamstabilizer used in the conventional ways of adding and mixing it intogypsum slurry directly, and consequently, the production cost for aweight-saved gypsum board product can also be reduced.

EXAMPLES

Next, the present invention is further illustrated specifically by usingexamples and comparisons.

(Gypsum Materials)

In regard to reference 1, examples 1 through 3, and comparison 1described below, a gypsum material was used in which a plurality ofgypsum raw materials with the following kinds and compounding ratioswere uniformly compounded. Also, in regard to reference 2, example 4,and comparison 2, only the following natural gypsum was used as a gypsummaterial.

Natural gypsum: 50 parts by weight

Phosphogypsum: 15 parts by weight

Fluorogypsum: 10 parts by weight

Flue gas desulfurized gypsum: 20 parts by weight

Waste recycle gypsum: 5 parts by weight

Additionally, the representative vales measured by chemical analysis forthe gypsum raw materials were as follows.

Natural gypsum: the purity of dihydrate gypsum 93%, CaCO₃ 3.5%, SiO₂ 3%,R₂O₃ and others 0.5%, pH 6.2 (wherein R represents Al and Fe, etc.,which is also applied hereinafter.)

Phosphogypsum: the purity of dihydrate gypsum 98%, total P₂O₃ 0.3%,fluorine 0.4%, SiO₂ 0.5%, R₂O₃ and others 0.4%, pH 4.1

Fluorogypsum: the purity of dihydrate gypsum 91%, SiO₂ 1%, R₂O₃ andothers (mainly anhydrous gypsum) 8%, pH 6.0

Flue gas desulfurized gypsum: the purity of dihydrate gypsum 98%, SiO₂0.6%, R₂O₃ and others 1.4%, pH 6.1

Waste recycle gypsum: the purity of dihydrate gypsum 90%, papercomponents 6%, R₂O₃ and others 4%, pH 6.3

(Foaming agent) Alkyl ether sulfate (produced by Toho Chemical IndustryCo., Ltd.)

(Hardening accelerator) 2.8 parts by weight of dihydrate gypsum and 0.2parts by weight of potassium sulfate

(Pore Size Adjusting Agents)

Agent for increasing foam size: aluminum sulfate (extra pure reagent,produced by Daimei Chemical)

Agent for decreasing foam size: sulfosuccinate-type surface active agent(KOHACOOL L-300 produced by Toho Chemical Industry Co., Ltd.)

[Reference 1]

100 parts by weight of calcined gypsum obtained by calcining a gypsummaterial that contains the gypsum raw materials described above, 85parts by weight of water, and 3.0 parts by weight of hardeningaccelerator were kneaded using a commonly used pin mixer so as to obtaingypsum slurry. Air was injected into an aqueous solution of the foamingagent stock solution that is described above using a spiral pump as afoaming apparatus so as to obtain foams. A foam addition port wasprovided on a slurry discharging part of the pin mixer and the foamswere added and mixed into gypsum slurry that outflows from the slurrydischarging part so as to obtain foamed gypsum slurry. On the otherhand, a portion of the obtained gypsum slurry described above wasfractionated and applied on a surface of a front-side base paper forgypsum board previously using a roll coater and the foamed gypsum slurrywas poured into a space between the front-side and a back-side basepapers for gypsum board so as to manufacture a board-shaped andweight-saved gypsum board with a thickness of 12.5 mm (a width of 910mm, a length of 1820 mm, and a density of 0.65 g/cm³). The amount ofslurry retained in a gypsum board shaping machine was controlled so thatit is kept substantially constant volume.

Then, one of the manufactured weight-saved gypsum boards was randomlysampled and test pieces for adhesion test, bending test, and corestrength test were sampled from the weight-saved gypsum board. A testpiece for SEM (scanning electron microscope) observation was sampledfrom the center portion of the remaining fragment of the weight-savedgypsum board along the width direction. In those tests, the adhesiontest and the SEM observation were performed just before sampling eachtest piece and the remaining tests were performed after drying in adryer at the temperature of 40° C. for 24 hours. The methods of therespective tests are described below.

(Adhesion Test)

A test piece with a total width of 910 mm and a length of 300 mm wassampled from one surface of the randomly sampled weight-saved gypsumboard. Then, a break along the width direction across the total width ofthe test piece was made on a back surface paper of the test piece usinga cutter. Then, the test piece was bent in a direction opposite to thesurface having the break and the test piece was stretched along thedirection so that force was applied uniformly along the width directionso as to be separated from a front surface paper fully. Afterward, thesurface area of an adhering part of the base paper for gypsum board (thefront surface paper) with a gypsum core of the test piece was measured,the rate of which (surface area ratio) (represented by %) wascalculated. Likewise, an adhering test in regard to the back surface ofthe same test piece was performed and the surface area ratio(represented by %) of an adhering part was also calculated. These ratiosof the surface area of an adhering part between the base paper forgypsum board and the gypsum core to the surface area of the test pieceon the one side, which are represented in percent, were regarded as theresults of the adhesion test.

(Bending Test)

The bending test for the test piece of the sampled weight-saved gypsumboard was performed based on the JIS A6901 standard.

(Core Strength Test)

The core strength test for the test piece of the sampled weight-savedgypsum board was performed based on ASTM C473-00“nail drawing resistancetest”.

(SEM Observation)

A fracture plane of the gypsum core of the test piece was observed usinga magnifier after the bending test. Furthermore, gold wasvapor-deposited on a part with a representative pore structure accordingto a common method and the part was observed using an SEM.

The test results are shown in FIG. 1 and Table 1.

TABLE 1 Adhesion Properties (Front Nail surface/ Breaking load (N)drawing Back Horizontal Vertical resistance surface) direction direction(N) Reference 1 100/100 580 230 411 Example 1 100/100 590 240 428Example 2 100/100 590 230 425 Example 3 95/95 550 220 400 Comparison 1100/100 570 230 416 Reference 2  90/100 530 200 362 Example 4 100/100550 220 370 Comparison 2 20/20 510 190 359

Example 1

A weight-saved gypsum board with a thickness of 12.5 mm (a width of 910mm, a length of 1820 mm, and a density of 0.65 g/cm.sup.3) wasmanufactured similar to reference 1 except adding 0.0005 parts by weightof aluminum sulfate as a pore size adjusting agent for increasing thesize of pores formed by bubbles in the foamed gypsum slurry per 100parts by weight of the calcined gypsum into the aqueous solution of thefoaming agent stock solution, and blowing air into the aqueous solutionof the foaming agent stock solution that contains aluminum sulfate so asto produce a foam having bubbles with the desired pore size. Also, oneof the manufactured weight-saved gypsum boards was randomly sampled andtests similar to those of reference 1 were performed. The results areshown in FIG. 2 and Table 1.

From the result of an SEM observation shown in FIG. 2, it will beunderstood that the weight-saved gypsum board of Example 1 has poreslarger than the pores in the weight-saved gypsum board of Reference 1.

Example 2

A weight-saved gypsum board with a thickness of 12.5 mm (a width of 910mm, a length of 1820 mm, and a density of 0.65 g/cm.sup.3) wasmanufactured similar to reference 1 except adding 0.005 parts by weightof aluminum sulfate as a pore size adjusting agent for increasing thesize of foams in the foamed gypsum slurry per 100 parts by weight of thecalcined gypsum into the aqueous solution of the foaming agent stocksolution, and blowing air into the aqueous solution of the foaming agentstock solution that contains aluminum sulfate so as to produce a foamhaving bubbles. Also, one of the manufactured weight-saved gypsum boardswas randomly sampled and tests similar to those of reference 1 wereperformed. The results are shown in FIG. 3 and Table 1.

From the result of an SEM observation shown in FIG. 3, it will beunderstood that the weight-saved gypsum board of Example 2 has poreslarger and more stable than the pores in the weight-saved gypsum boardof Example 1.

Example 3

A weight-saved gypsum board with a thickness of 12.5 mm (a width of 910mm, a length of 1820 mm, and a density of 0.65 g/cm.sup.3) wasmanufactured similar to reference 1 except adding 0.003 parts by weightof the sulfosuccinate-type surface active agent as a pore size adjustingagent for decreasing the size of pores formed by bubbles in the foamedgypsum slurry per 100 parts by weight of the calcined gypsum into theaqueous solution of the foaming agent stock solution, and blowing airinto the aqueous solution of the foaming agent stock solution thatcontains the sulfosuccinate-type surface active agent so as to produce afoam having bubbles. Also, one of the manufactured weight-saved gypsumboards was randomly sampled and tests similar to those of reference 1were performed. The results are shown in FIG. 4 and Table 1.

From the result of an SEM observation shown in FIG. 4, it will beunderstood that the weight-saved gypsum board of Example 3 has poressmaller and more stable than the pores in the weight-saved gypsum boardof Reference 1.

[Comparison 1]

In the weight-saved gypsum board disclosed in Japanese Laid-Open PatentApplication No. 10-330174, 85 parts by weight of water, 3.0 parts byweight of hardening accelerator and 0.3 parts by weight of aluminumsulfate as the foam stabilizer per 100 parts by weight of calcinedgypsum were kneaded using a commonly used pin mixer so as to obtaingypsum slurry. A portion of the obtained gypsum slurry was applied on asurface of a front-side base paper for gypsum board using a methodsimilar to Example 1. A foam addition port was provided on a slurryextracting part of the pin mixer and the foams produced from the aqueoussolution of the foaming agent stock solution were added and mixed intothe gypsum slurry so as to obtain foamed gypsum slurry. The foamedgypsum slurry was poured into a space between the front-side and aback-side base papers for gypsum board so as to manufacture aboard-shaped and weight-saved gypsum board with a thickness of 12.5 mm(a width of 910 mm, a length of 1820 mm, and a density of 0.65 g/cm³).

Also, one of the manufactured weight-saved gypsum boards was randomlysampled and tests similar to those of reference 1 were performed. Theresults are shown in FIG. 5 and Table 1.

The weight-saved gypsum board in Comparison 1 is comparable with theweight-saved gypsum board in Example 1 in regard to the adhesionproperties, the flexural strength, and the pore sizes, etc. However, theloading of aluminum sulfate used as the pore size adjusting agent inExample 1 was 0.0005 parts by weight and the loading of aluminum sulfateused as the pore size adjusting agent in Example 2 was 0.005 parts byweight whereas the loading of aluminum sulfate used as the foamstabilizer in Comparison 1 was 0.3 parts by weight. That is, it will beunderstood that the loadings of the pore size adjusting agents used inExample 1 and Example 2 are very little compared to the loading of thefoam stabilizer used in Comparison 1. In accordance with the method ofmanufacturing a weight-saved gypsum board of the present invention, theloading of the pore size adjusting agent can be significantly reducedcompared to the loading of the foam stabilizer in the conventionaltechnique, so that the production cost for a weight-saved gypsum boardcan also be reduced. Additionally, when other pore size adjusting agentsare used, similar results may be obtained.

In the above-mentioned examples, a method of manufacturing aweight-saved gypsum board according to the present invention was appliedto a weight-saved gypsum board made from a gypsum material obtained bycompounding several kinds of gypsum raw materials. A method ofmanufacturing a weight-saved gypsum board according to the presentinvention can also be applied to a weight-saved gypsum board made from agypsum material that contains only one kind of gypsum raw material asdescribed below.

[Reference 2]

Foams were obtained by injecting air into an aqueous solution of afoaming agent stock solution using a spiral pump as a foaming apparatus.Then, the foams were mixed into 100 parts by weight of calcined gypsumobtained by calcining only the natural gypsum described above, 85 partsby weight of water, and 3.0 parts by weight of hardening acceleratorusing a commonly used pin mixer so as to prepare foamed gypsum slurry.Then, a board-shaped and weight-saved gypsum board with a thickness of12.5 mm (a width of 910 mm, a length of 1820 mm, and a density of 0.65g/cm³) was manufactured from the foamed gypsum slurry according to acommon method. Also, one of the manufactured weight-saved gypsum boardswas randomly sampled and tests similar to those of reference 1 wereperformed. The results are shown in FIG. 6 and Table 1.

Example 4

A weight-saved gypsum board with a thickness of 12.5 mm (a width of 910mm, a length of 1820 mm, and a density of 0.65 g/cm.sup.3) wasmanufactured similar to reference 2 except adding 0.0005 parts by weightof aluminum sulfate as a pore size adjusting agent for increasing thesize of pores formed by bubbles in the foamed gypsum slurry per 100parts by weight of the calcined gypsum into the aqueous solution of thefoaming agent stock solution, and blowing air into the aqueous solutionof the foaming agent stock solution that contains aluminum sulfate so asto produce a foam having bubbles. Also, one of the manufacturedweight-saved gypsum boards was randomly sampled and tests similar tothose of reference 1 were performed. The results are shown in FIG. 7 andTable 1.

[Comparison 2]

According to the conventional technique claimed in claim 12 in JapanesePatent No. 3028123, alkyl sulfate having the chemical formularepresented in the claim was diluted with water so as to prepare anaqueous solution. Then, air was blown into the prepared aqueous solutionso as to produce a foam having bubbles with a form density of 0.205g/cm.sup.3 The produced foams were added and mixed into gypsum slurryfractionated from the slurry extracting part using a method similar toExample 1 so as to obtain foamed gypsum slurry. The foamed gypsum slurrywas poured into a space between a front-side and a back-side base papersfor gypsum board so as to manufacture a board-shaped and weight-savedgypsum board with a thickness of 12.5 mm (a width of 910 mm, a length of1820 mm, and a density of 0.65 g/cm.sup.3). Also, one of themanufactured weight-saved gypsum boards was randomly sampled and testssimilar to those of reference 1 were performed. The results are shown inFIG. 8 and Table 1.

The weight-saved gypsum board of Example 4 obtained by applying a methodof manufacturing a weight-saved gypsum board according to the presentinvention to a weight-saved gypsum board made from a gypsum materialthat contains a single gypsum raw material has pores with larger sizesand significantly improved adhesion properties compared to theweight-saved gypsum boards in Reference 2 and comparison 2.

From the above-mentioned results, when the gypsum material contains onlyone kind of a natural gypsum as well as when the gypsum material isobtained by compounding several kinds of gypsum raw materials, thestructure of pores in a gypsum core, that is, the sizes of the pores inthe gypsum core can be adjusted timely and freely by mixing foamsproduced from a foaming agent that contains a pore size adjusting agentinto gypsum slurry that contains water and calcined gypsum obtained bycalcining the gypsum material that contains the gypsum raw material(s).

Additionally, the present invention is not limited to the examplesdescribed above and the examples described above can be improved andmodified within the scope of the present invention.

1. A method of manufacturing weight-saved gypsum board in which poreswith a predetermined size are distributed in a gypsum core, comprisingthe steps of: blowing air into a foaming agent to produce a foam havingbubbles; mixing the foam having bubbles into a kneaded material thatcontains calcined gypsum and water to obtain foamed gypsum slurry;pouring the foamed gypsum slurry into a space between upper and lowerpapers for gypsum board; shaping the base papers and the foamed gypsumslurry into a board shape; roughly cutting off and subsequently dryingthe board shape; and cutting off the dried board shape into a productdimension; wherein the method further comprises the step ofpreliminarily adding a pore size adjusting agent for adjusting sizes ofpores formed by bubbles distributed in the foamed gypsum slurry to oneof a stock solution of the foaming agent and a mixture of a stocksolution of the foaming agent and water to obtain the foaming agent forproducing a foam having bubbles with desired sizes; wherein the poresize adjusting agent contains at least one substance selected from thegroup consisting of agents for decreasing sizes of pores formed bybubbles in the foamed gypsum slurry; and the agent for decreasing sizesof pores formed by bubbles in the foamed gypsum slurry contains at leastone substance selected from the group consisting of sulfosuccinate-typesurface active agents, sarcosinate-type surface active agents,alkylbenzene sulfonate-type surface active agents, alkane sulfonate-typesurface active agents, and alkylbetaine-type surface active agents. 2.The method of manufacturing a weight-saved gypsum board as claimed inclaim 1, wherein in a content of the pore size adjusting agent in thefoaming agent is 0.00001 parts by weight through 0.005 parts by weightper 100 parts by weight of the calcined gypsum.
 3. A method ofmanufacturing a weight-saved gypsum board in which pores with apredetermined size are distributed in a gypsum core, comprising thesteps of: blowing air into a foaming agent to produce a foam havingbubbles; mixing the foam having bubbles into a kneaded material thatcontains calcined gypsum and water to obtain foamed gypsum slurry;pouring the foamed gypsum slurry into a space between upper and lowerbase papers for gypsum board; shaping the base papers and the foamedgypsum slurry into a board shape; roughly cutting off and subsequentlydrying the board shape; and cutting off the dried board shape into aproduct dimension; wherein the method further comprises the step ofpreliminarily adding a pore size adjusting agent for adjusting sizes ofpores formed by bubbles distributed in the foamed gypsum slurry to oneof a stock solution of the foaming agent and a mixture of a stocksolution of the foaming agent and water to obtain the foaming agent forproducing a foam having bubbles with desired sizes; wherein the poresize adjusting agent contains at least one substance selected from thegroup consisting of agents for increasing sizes of pores formed bybubbles in the foamed gypsum slurry; and the agent for increasing sizesof pores formed by bubbles in the foamed gypsum slurry contains at leastone substance selected from the group consisting of sulfuric acid,sulfamic acid, sodium hydroxide, and potassium hydroxide.
 4. The methodof manufacturing a weight-saved gypsum board as claimed in claim 3,wherein a content of the pore size adjusting agent in the foaming agentis 0.00001 parts by weight through 0.005 parts by weight per 100 partsby weight of the calcined gypsum.
 5. The method of manufacturing aweight—saved gypsum board as claimed in claim 3, wherein the agent forincreasing sizes of pores formed by bubbles in the foamed gypsum slurrycontains at least one substance selected from the group consisting ofsulfuric acid, sulfamic acid, and potassium hydroxide.